What does "pissy butt" mean here? [closed]

It means the kid had urine on his behind, because he had peed himself in bed.

pissy

adj.
Irritable; cranky.
adj.
Covered in piss.
adj.
Resembling or smelling like piss.

piss

noun

Definition of piss (Entry 2 of 2)

1 usually vulgar : urine

butt

noun (1) \ ˈbət \ Definition of butt

(Entry 1 of 6)

1 : buttocks

slipped and fell on his butt